Modern RF transmitters support a variety of frequency bands. A transmitter for a mobile telecommunication network being compatible with several of the Third Generation Partnership (3GPP) standards may require support for the following bands or frequency ranges:                4 Low Bands between 698 . . . 915 MHz, Band 5, 6, 8, 12, 13, 14, 17, 18, 19, 20, 26, 27, 28, 44.        3 Mid Bands, Band 11 and 21 at 1428 . . . 1463 MHz plus band 24 at 1626 . . . 1661 MHz.        14 High Bands between 1710 . . . 2025 MHz.: Band 1,2,3,4,9,10, 23,25, 33,34,35,36,37,39.        5 Bands around 2.5 GHz between 2300 . . . 2690 MHz.: Band 7, 30,38,40,41.        2 Bands around 3.5 GHz between 3400 . . . 3800 MHz.: Band 42 and 43.        4 GSM Bands.        
Given that a ratio between the lowest and the highest supported frequency range of a single Controlled Oscillator (DCO) is typically around 1.3 to 1.4, multiple DCO's are required to fulfill such a compatibility requirement. For polar transmitters also the instantaneous frequency modulation range has to be considered, further reducing the supported range of carrier frequencies of a single DCO. To support one or several transmission bands, each DCO additionally requires an associated Digital to Analog Converter (DAC) and an upsampling filter chain. In summary, the more DCO's are used, the more engineering time is needed to design, layout, test and verify the associated transmit (Tx) chains, each consisting of wiring, digital filter, DCO and DAC. Additionally, each transmit chain requires a considerable amount of chip area and contributes to the overall power consumption.
It would be beneficial to reduce the number of DCO's to save on chip area, production cost, and engineering time for design, layout, test and verification.